I am just making a SWAG based on the color. The crop appears to be a mixture of break and yeast. I am being conservative by estimating that the the crop contains approximately 50% yeast cells (the percentage could be higher), which should be around 1.2 billion cells per milliliter. The only way to know for certain is to count. However, as I have mentioned before, yeast cultures are like nuclear weapons in that one does not need pin-point accuracy in order to get the job done. Two hundred milliliters of that stuff should fully attenuate 5 gallons of 1.072 wort without batting an eye. Heck, 150 milliliters should do the job.

S. cerevisiae

A 2L starter will provide a substantial margin of error for 5-gallons of 1.070 wort. However, a starter is a waste of time with that much yeast slurry at your disposal. All you need to do is to pitch 5 to 6 fluid ounces of that stuff.